Technical Definition:

1 – 2 Shift

Technical Description:

On vehicles with electronically controlled automatic transmissions, the 1-2 shift solenoid is responsible for actuating the hydraulic circuits to activate clutches or bands that change gears inside the automatic transmission. The shift solenoids are controlled by either a Transmission Control Module (TCM), or the Engine Control Unit / Powertrain Control Module (ECU / PCM). The control circuit may be power or ground side controlled depending on the application.

Possible Causes:

• 1-2 shift solenoid failure
• Electrical short to power – pinched wires
• Electrical short to ground – pinched wires
• Open in power or ground circuit wiring – disconnected or loose connections
• TCM or PCM internal failure

Possible Symptoms:

• Check engine light illuminated
• Vehicle will not shift from 1st to 2nd gear

1-2 Shift Malfunction

Possible Solutions:

• Disconnect PCM or TCM wiring harness, depending on the application and using an electrical diagram as reference, check for excessive resistance or an open in the control circuit. Using a Digital Volt Ohm Meter (DVOM) set to the Ohms scale, check for resistance on the 1-2 solenoid power and ground sources to determine if there is an open circuit or excessive resistance in the 1-2 solenoid. Visually inspect for for any pinched, disconnected or loose wires on the harness connectors.
• Short to power: Disconnect battery positive cable and wiring harness connector at transmission and check for continuity using the DVOM between power source and solenoid circuit wiring in key on / engine off (KOEO) position as well as the key off position.
• Short to ground: Disconnect battery positive cable and wiring harness connector at transmission and check for continuity using the DVOM between 1-2 solenoid power source and a known good ground.
• TCM or PCM failure: Using an advanced scan tool capable of controlling solenoids, manually activate the 1-2 shift solenoid. It may be necessary to manually activate transmission control relay on some vehicles if power is not present at the transmission wiring harness connector. If a scan tool is not available, it will be necessary to monitor the 1-2 solenoid circuit to determine if the TCM or PCM is sending a power or ground signal to the 1-2 solenoid during vehicle operation.

OBD-II Trouble Code Type:

Diagnostic Step:

Tech Notes:

– Low transmission fluid level
– Dirty transmission fluid
– Faulty shifting solenoid valve
– Shifting solenoid valve harness is open or shorted
– Shifting solenoid valve circuit poor electrical connection

Specific Makes:

– Transmission may not shift to the next gear.